Question

Why is a CNS neuron not usually replaced after it is injured?

Classify neurons according to their function?

_______ account for roughly half of the volume of the nervous system.

Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because:

identify the neuroglia of the peripheral nervous system.

Answer 1

Answer

1) In peripheral nervous system, the axons have a covering of membrane called neurilemma.
  This membrane helps in regenration of nerves.
The neurons in CNS do not contain neurilemma. Hence, these neurons cannot be replaced and the damage is permanant.

2) There are three types of neurons based on function :

a) Sensory neuron : They send impulse from body organs / tissues towards the central nervous system.

b) Motor neuron : They send impulses from central nervous system towards the body organs.

c) Interneurons : They form a connection between sensory and motor neurons.

3) Neuroglia account for roughly half of the volume of the nervous system.

4) Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because : Blood brain barrier formed by astrocytes do not allow penetration of drugs or medication into the CNS.

5) There are two types of neuroglia in peripheral nervous system :

a) Satellite cells : They provide cushioning and physical support to neurons of PNS.

b) Schwann cells : They form myelin sheath around axons of PNS. They also help in regeneration of damaged nerves.